Research Of The Temperature-dependent Mechanical Property Of Adhesive Interface Between EPDM Films

Ethylene propylene diene monomer (EPDM) rubber film has been widely used as an inhibitor to control the burning face of the solid propellant and protect the motor case against the high-temperature combustion-gas resulting from the burning propellant in free-filling grain solid rocket motors. If the combustion-gas spurt into the voids and microcracks at the interface between EPDM films, this may leads to debonding of the interface and the structural integrity of motor fails, which may affect serviceability of the motor or even cause the motor to explode. In this paper, we set the bonding interface between EPDM films as the research target, studied the mode I fracture behavior of the bonding interface with experimental and numerical methods.(1) The experimental methodology and specimen manufacture of the mode I fracture experiments of the bonding interface between EPDM films. Took account of the teature of EPDM and referred to the relevant paper, we made a feasible experimental method, that was obtain the interface fracture energy with double cantilever sandwich beam(DCSB) experiment, using uniaxial test obtain fracture strength of the interface, a temperature test chamber was used to simulate the temperature that the bonding interface suffers in the storage and transport of the rocket motors. At last, the specimens were manufactured.(2) The temperature-independent mode I fracture behavior of the bonding interface. Carried out mode I fracture experiment and analysed the feature of the bonding interface during the fracture process. Obtained interface fracture energy by simple beam theory(SBT), correct beam theory(CBT) and experiment compliance method(ECM), and the fracture strength of the interface. Then used the temperature-independent bilinear cohesive zone model(CZM) that using the obtained fracture energy and strength as its parameters, to simulate the mode I fracture behavior of the DCSB specimen, the deviation between numerical and experimental results demonstrates that the obtained fracture paramters were not accurate, thus, an inverse analysis method based on Hookes-Jeeves algorithm was used and odtained accurate fracture parameter of the interface. Through the comparison of numerical and experimental results, we got the conclusion that CBT and ECM can be used to determine relatively accruate fracture energy of the interface.(3) Experimental research on the temperature-dependent fracture behavior of the bonding interface. The temperature-dependent DCSB and uniaxial test were performed in the temperature test chamer. Then analysed temperature-dependence of the load-displacement curves, and the fracture feature of the specimens that tested at different temperatures. According to the observed experimental phenomena of the specimens, we get that the bonding strehgth between EPDM and adhesive is lower than the fracture strength of adhesive. At last, used compliance-based beam method(CBBM) calculated the mode I fracture energy of the bonding interface.(4) Construction of temperature-dependent mode I fracture model of the bonding interface. The temperature-dependent fracture model was established based on temperature-independent CZM. Fracture parameters of the bonding interface at different temperatures were obtained using the inverse analysis method that based on numerical and experimental methods, and calculated the parameters of the temperature-dependent fracture model. These parameters showed temperature-dependency, then fitting them and obtained temperature-dependent cohesive law, thus, the temperature-dependent model was established. At last, the accuracy of the model was verified by four experiments at other temperatures.In this paper, the mode I fracture behavior of the interface between EPDM films was researched with the method of combing experiment and numerical simulation. A model which can be used to describe the temperature-dependent fracture behavior of the bonding interface was contructed. This study offers a theoretical basement for the design and numerical simulation of the grain in the SRMs in future.